The supposedly-imagined dream of YGB in which he saw a witches Sabbath, the baptism into the "mystery of sin", the evil man, and all the other rituals, had a real effect on him as a person both physically, psychologically, socially, and most importantly spiritually. An event which supposedly takes place in the mind can in fact effect a person to the point of physical danger which is the whole idea behind YGB: That the sins of the mind and the sins of the soul, though abstract, can cause concrete effects in all humans the way that sin can endanger and affect our bodies through poisoning our minds and souls.

To answer concisely, it is the combination of the visible and the invisible working together concretely which makes the imaginary and the real have a working relationship.